Sleep Apnea Not Detrimental to Some Young Air Force Personnel
20-Sep-2005 11:00 AM EDT
Newswise — A new study finds that young Air Force men and NFL players have some similar qualities. They exercise regularly, often at body-building, they develop muscle mass in the arms and neck; and they may have obstructive sleep apnea, a disease that can be debilitating and even fatal.
Background: A good night's sleep is critical for the best physical and mental performance. Alertness and physical stamina can deteriorate if sleep is acutely or chronically disturbed. A serious disturbance of a good night's rest is obstructive sleep apnea (OSA), a common clinical disorder affecting four percent of the general population. OSA is clinically defined by frequent periods of absence of breathing, or shallow breathing, leading to sleep disruption. The result is significant morbidity, ranging from automobile accidents to substantial cardiovascular disease. Previous research suggests that sleep deprivation may result in decreased exercise performance. However, there is limited published research on the overall affects sleep apnea OSA has on exercise tolerance.
A measurement of exercise performance can be found in aerobic exercise, which involves improving oxygen consumption by the body. The most accurate test of aerobic fitness involves the measurement of maximal rate of oxygen consumption (VO2max). VO2max is the maximum amount of oxygen consumed and is measured in milliliters per kilogram of body weight per minute. Submaximal exercise testing, using cycle ergometry testing has been used as a reliable means to estimate VO2max. The United States Air Force (USAF) has used the VO2max test since 1992 as the standard method to monitor the fitness level of their personnel.
A new retrospective study set out to determine if USAF members with OSA demonstrated objective differences in aerobic fitness as measured by cycle ergometry when compared to the general USAF population. The researchers also sought to determine if surgical intervention or medical therapy with CPAP improved VO2max. The authors of "Does Obstructive Sleep Apnea Affect Aerobic Fitness?" are Louis Q. Guillermo, M.D., Major, USAF, MC; Thomas J. Gal, M.D., M.P.H., Major, USAF, MC; and Eric A. Mair, M.D., F.A.A.P., Colonel, USF, MC; all from the Department of Otolaryngology-Head and Neck Surgery, Wilford Hall USAF Medical Center, Lackland AFB, TX. Their findings will presented at the109th Annual Meeting and OTO Expo of American Academy of Otolaryngology—Head and Neck Surgery Foundation, September 25 " 28 at the Los Angeles Convention Center, Los Angeles, CA.
Methodology: All active duty USAF personnel were required to undergo annual cycle ergometry testing between January 1, 1999 and December 31, 2003. Mean ergometry scores for this population were obtained from the databases at the Population Health Support Division at Brooks Air Force Base (AFB), TX. Mean VO2max was available for each year, classified by age and gender, providing a composite of over 290,000 annual ergometry tests, for a total of nearly 1.4 million (1,399,174) ergometry tests scores.
Some 247 active duty USAF personnel were identified as having undergone laboratory-based multichannel polysomnography (sleep study) at Wilford Hall Medical Center, Lackland AFB, TX. Patient age at the time of sleep study (PSG), date of PSG, apnea-hypopnea index (AHI), gender, and body mass index (BMI) were obtained from the sleep center records. Sleep center records were also used to determine if a CPAP device was recommended and used. Additionally, patients who underwent OSA related surgery were documented.
Cycle ergometry scores for the 247 OSA patients were obtained from data at the Population Health Support Division at Brooks AFB, TX. Comparisons of mean ergometry scores for the OSA cohort with PSG data were compared to mean scores from the normative data using 2-tailed Student's t-test. Gender, age group, and severity of OSA further stratified comparisons across groups.
Results: All patients were between the ages of 17 and 54, with a mean of 36.6Â±8.0 years. The majority of patients were male (88.3 percent). OSA severity was uniformly distributed across all categories, although the majority of females were classified as having mild OSA. 42 patients (17 percent) underwent 57 OSA-related surgical procedures; 117 patients (48.2 percent) were recommended for CPAP.
In this study population, patients with moderate to severe OSA (AHI>20) demonstrated a statistically significant difference in fitness level as measured by cycle ergometry. The clinical significance of these findings, however, is more difficult to define. When adjusting for age and gender, many sub-groups with sleep apnea in this study actually scored higher than normative values of the entire Air Force population. This may reflect a subgroup of patients with sleep apnea uniquely represented in the Armed Forces: They are younger, and often exceedingly physically fit, presenting with OSA only as a function of increased upper airway muscle mass. The older, more obese patients, probably more classically thought of in adult sleep apnea, are largely underrepresented in the military population. A greater percentage of patients with an increased BMI likely had increased muscle mass from weightlifting and other physical training, rather than sedentary obesity. The qualities that make a professional soldier formidable on the battlefield (increased BMI due to upper body muscular hypertrophy with large muscular necks) can leave the young combatant gasping for breath during sleep.
A significant aspect of this study is that consenting to a sleep study in the active duty military can have adverse career implications that may deter additional patients from seeking medical attention for sleep apnea. Personnel identified with OSA by PSG are frequently unfavorably limited in terms of assignments and deployablility, due to the need for CPAP and its limited utility under field conditions. Thus many personnel opt not to undergo evaluation for sleep disordered breathing, or seek surgical options without PSG documentation. While patients in this study represent only those seeking attention at a single military medical facility, the true number of patients with sleep apnea is likely underrepresented.
Conclusions: Overall, in a young Air Force population, mild OSA does not predict a decrease in aerobic fitness as measured by cycle ergometry. However, those patients with moderate to severe OSA (AHI >20) have a statistically significant decrease in aerobic fitness compared to the normal population. Changes in aerobic fitness measurements between control patients and mild OSA patients may be masked or attenuated by the overall healthy, physically fit status of the military personnel studied. However, once moderate to severe OSA was noted, aerobic fitness scores statistically declined.